Espritmodel.com Telemetry Radio
Reply
Thread Tools
This thread is privately moderated by maguro, who may elect to delete unwanted replies.
Old Jul 06, 2012, 01:39 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,695 Posts
Quote:
Originally Posted by Flyboy Steve View Post
Hi guys!

I've been using gorilla glue to lamlinate EPP foam layers together to make the KF airfoils.

GG is sure hard to spread in a very thin layer.

Does anybody know of something I can use to THIN it before application, and that won't hurt the EPP foam?

I like GG because it seems that when it "foams up", it penetrates the cells and pores of the foam and really locks it together. Is there an ALTERNATIVE glue that also does this but is more easily spread?

Thanks!
I put it down in serpentine strings that are may be 1/8" or so wide and maybe 1-2" apart. Then I spread it with a plastic spreader/scraper cut from a plastic can lid. I usually spritz the foam with a fine spray plant mister before I put the GG on and spread it and the water and glue get mixed a little in the spreading process. I look for an even shiny surface on one of the two pieces and then bring them into contact and weight them. On some pieces where I want to make sure of a good bond along the edges for like leading or trailing edges or wing tips I'll put a little extra bead there and spread it.

And I nearly always weight the entire glued area and/or clamp them to keep pieces from shifting and I think that also increases the penetration maybe.

The GG Quick, the white stuff, is my mainstay. I really like it. I also use some Elmers brown PU glue that sets slowly for some things that have larger areas and that will be left overnight to set up.

Any area that will be taped for coloring and that does not have the plastic skin still on it gets a light dusting with 3M 77 ($12 a can) or Duro 0188 General Purpose aerosol adhesive ($4 a can). For skin on areas the tape is applied to the skin.

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Sign up now
to remove ads between posts
Old Jul 06, 2012, 03:51 PM
Watt Waster
Tsavah's Avatar
Joined Oct 2010
1,808 Posts
Making Foaming Glue Thin - Laminating EPP, or ...

Interesting question, but not uncommon when looking for ways to laminate EPP, or another type of foam board. Lots of folks have different ways to laminate EPP, or another foam type when they are wanting a KFm airfoil, fuselage, or another objective. The foaming glues like the Gorilla brand can be thinned, or more accurately, pre-foamed in water. All you need is a mixing cup of the appropriate size to do the mixing in. Put the water in first, then add the glue, estimating how much you will need, and start stirring. The glue will not actually mix into the water like one might expect, but the chemical reaction will begin. In a short time, as in 4-8 minutes, the glue will begin to foam, turning from the amber (or clear) color, to a tan (or slightly white) foam around 30%-50% greater in volume. If you worked quickly enough spreading the glue on one surface, the foaming will continue for around 10 minutes more, depending on how long you stirred, room temperature, and moisture in the air. Before the 10 minutes turns the pre-foamed glue into a hardening bonding agent, you want to press the lamination together and place a very flat compressing object on top. I like to use a thick piece of glass and add a few "freezer" Ziploc sandbags.

I normally leave the lamination alone for at least a few hours so the foaming has stopped while under pressure between two pieces of thick glass. It is hard to have a better pressing system since glass isn't likely to warp in the next 20 or more years when stored flat, or on one side to prevent breakage. The key is to work fast, but you may find that difficult to master because as the foaming glue starts to react with water, it gets thicker and hard to spread evenly. The only way to get around the issue is to spray it, but that will gum up the sprayer, and the foaming glue is just too thick. One hint on how to thin the glue is the fact alcohol products thin it and that is how I clean up my spreaders and brushes. Another hint is a damp cloth allows one to spread the glue on it, and into the fibers. The catch is you end up using a lot of glue and once it has cured/hardened, it is very difficult to sand, or otherwise make smooth. What you can do is find a mix ratio of alcohol (or another chemical) and foaming glue you like best and apply it to one surface with a brush or spreader (flexible plastic, like a puddy knife, or old gift card) as evenly as possible within the given working time before pressing the two foam surfaces together.

The reason I know about this is I also prefer the foaming glues when making a foam airplane fuselage or wing. I use alcohol on a paper towel piece to wipe down the excessive foaming out of the joint once every six-seven minutes, two or three times before I apply masking tape to hold any additional excess foaming within a confined space. I hold off on applying the masking tape until the alcohol has evaporated from the surface (around three to four minutes) and the excess foaming appears to be nearly finished because the glue has developed a hardened skin/surface. If you are doing simple, flat lamination, you can take a hint from screen printed T-shirt folk and set up a very similar process for getting the foaming glue on the first surface, but without the need for a screen. Place the foam sheet in a frame to keep it in place, and put glue on one end, then use a wide enough wiper to spread it to the other end very thinly. You will have to practice a bit to get the glue spread evenly and thin enough to do the job without wasting the glue, and needing to clean up a lot of excessive foaming out of the lamination. The trick is to learn how little foaming glue gets the job done. You will also need thick glass under and on top of the lamination while it sets/cures. Foaming glues work/bond best when curing under adequate pressure, but not so much as to damage the foam board.

Just keep in mind the glue is very hard, to impossible to sand, and if you are wanting to sand the foam later, the glue is going to be an obstacle. There may be a way to pre-mix the glue with alcohol (or another chemical) to thin it and still get an adequate bond where the glue isn't so difficult to sand down. Most folks that make laminations with foam board use the green labeled (water cleanup) rubber cement products. The glue is said to make a very useful (contact cement) bond to foam without harming it and the cured glue sands away nearly as easily as the foam does. There are a number of RC Group threads that make wings and fuselages using a pre-cut lamination construction process. By pre-cutting the foam parts, very little cutting and sanding is needed later to finish the construction process. If you don't mind the extra work, you can laminate the thin foam board over a jig/fixture so once the glue has cured/set, the foam is already in the desired shape for the part needed. One example is called "baking a wing airfoil", but without the need to bake at 180- 200 degrees F for around 15 to 25 minutes. Instead you laminate the thin foam on the jig/fixture and once the glue has set/cured, the part is ready for use, or the next step of assembly.

Prior posts offering hints for good laminations are provided and can be used successfully with foam boards. Just remember to test your idea on scrap foam and look for application and construction method problems. The key to spray glue is how it is applied to foam. Most spray can glues attack foam because of the chemicals in the formula, but many of them can be applied as a fine mist if the glue is pre-mixed properly, warm, and mist coated from more than 8" away from the surface in a still air environment. In most applications you will need more than one mist coating with an adequate "dry-out" period between. All of them have health warnings on the label that need to be observed. You will also want to get out of a dumpster a large furniture box and turn it into a spray booth with an airflow away from you and outside to get the fumes out of your air. A simple box fan with a low setting to blow the air away from you and through a home air filter is often adequate, but don't pass the glue, or paint polluted air through the box fan motor. Sometimes the concentration of flammable fumes can cause an explosion, or fire, and at the very least, gum up the motor. Safety is always the first priority and think long term, rather than today. Dang, this has gotten kind of long winded again.
Tsavah is offline Find More Posts by Tsavah
Last edited by Tsavah; Jul 06, 2012 at 03:52 PM. Reason: Spelling ...
Reply With Quote
Old Jul 06, 2012, 04:57 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,695 Posts
Tsavah wrote:

"..Just keep in mind the glue is very hard, to impossible to sand, and if you are wanting to sand the foam later, the glue is going to be an obstacle..."

I haven't found that the case at all in using Gorilla Quick and other foaming PU glues on FFF. The foam is soft, sands easily and can even be shaped to act as a filler for under tape.

Expoxy and CA does not sand as well at all. On hot glue I try to shape it into curves or fillets as it is cooling and there is little that can be done to shape it after it set up hard.

And when it comes to hot glue, there is one that is clearly superior to all the others I have tried. That is the Arrow Brand #BSS6-4 High Strength and Slow Setting for Woodworking hot glue. It comes in 4" sticks and you can get it at Home Depot, Lowes, and similar places. It is applied at the High temp setting on a dual temp High/Low gun and you'll see wisps of smoke or steam arise from FFF as it is applied to a joint.

It will also stick well to the colored packing tape so you can cover two parts with colored tape (like a VSTAB to set on a HSTAB) and then use that hot glue to fillet weld the joint where the two meet and it will give you a very strong joint.

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Old Jul 16, 2012, 08:47 PM
Smells like SCIENCE!!!
ibillwilson's Avatar
Canada, ON, Toronto
Joined Jun 2012
341 Posts
He there everybody. I'm pretty new here, and I haven't read everybpost in this thread, but I havebskimmed a lot of it. I have a couple of questions that I hope you can help me with; if they've been dealt with before, please let me know and I'll go back to lurking.

Both questions deal with the issue of tip stall on a rectangular KFM3 wing with tip plates. I did not initially build in any washout, and I had horrible tip stall problems whenever I made a turn at slow speeds. I managed to totally solve the problem without tapering the wing... But while my intuition told me what to try, I don't know why these fixes worked.

Question 1. What effect arises from curling up the trailing edge corners at the locations of the tip plates?

Question 2. What is the effect of adding a small KF-like step to the bottom of the wing, at the leading edge corners at the tip plates?

These may just be general aerodynamics questions, but something is telling me that the physics of the KF airfoils is important here.

Thanks in advance!
ibillwilson is offline Find More Posts by ibillwilson
RCG Plus Member
Old Jul 16, 2012, 09:55 PM
Build straight - Fly twisty
Whiskers's Avatar
Australia, QLD, Little Mountain
Joined Feb 2010
4,172 Posts
I'm not 100% sure I understand your description (pix would help a lot) but I think both the things you mention would act a bit like wash-out.
Whiskers is online now Find More Posts by Whiskers
Reply With Quote
Old Jul 16, 2012, 10:44 PM
Smells like SCIENCE!!!
ibillwilson's Avatar
Canada, ON, Toronto
Joined Jun 2012
341 Posts
Quote:
Originally Posted by Whiskers View Post
I'm not 100% sure I understand your description (pix would help a lot) but I think both the things you mention would act a bit like wash-out.
Yes, sorry about the lack of pics and the convoluted descriptions. I'll be able to get pics tomorrow, which should clear things up.

Essentially, what I tried to do was approximate a twist of the wing at the wing tips, without actually twisting the wing. So, at both wingtips, I curl the the trailing edge up and slightly extend the leading edge down with a 1/2" chord strip, while leaving the rest of the wing as-is.
ibillwilson is offline Find More Posts by ibillwilson
RCG Plus Member
Old Jul 16, 2012, 11:28 PM
Build straight - Fly twisty
Whiskers's Avatar
Australia, QLD, Little Mountain
Joined Feb 2010
4,172 Posts
Yup! That's much as I thought, so my answer stands. (until such time that I see the pix, and then it may fall over )
Whiskers is online now Find More Posts by Whiskers
Reply With Quote
Old Jul 17, 2012, 08:16 AM
Smells like SCIENCE!!!
ibillwilson's Avatar
Canada, ON, Toronto
Joined Jun 2012
341 Posts
Quote:
Originally Posted by ibillwilson View Post
...

Question 1. What effect arises from curling up the trailing edge corners at the locations of the tip plates?

Question 2. What is the effect of adding a small KF-like step to the bottom of the wing, at the leading edge corners at the tip plates?

...
Finally, here are the pics. Aside from the two wingtip mods, I think this is a pretty normal KFM3 wing. It does have a tiny bit of dihedral, so I installed the tip plates at a slight angle, but I still don't think they're completely vertical when the wing is on the plane. The build material is Readiboard from my local Dollarama store, the overall wing dimensions are 30" x 6", and the KF steps are at 50% and 75%.

Plus, now that I have the pics, I can ask my other question. I want to do big Fowler flaps on this wing... Would it be okay to have the flaps be the last 25% of the wing chord, i.e. The entire panel aft of the 75% step?
ibillwilson is offline Find More Posts by ibillwilson
RCG Plus Member
Old Jul 17, 2012, 08:25 AM
Registered User
maguro's Avatar
United States, DE, Bear
Joined Apr 2007
1,560 Posts
Curling the trailing edge up acts as washout. It causes the tips to stall later than the wing root. Washout is very useful in delaying tip stall on high aspect ratio (long thin) wings and wings with a lot of taper.

The blunt strip on the bottom of the wing will cause turbulent air flow under the wing tip. The results will be high drag and decreased lift at the tip. I can't think of any aerodynamic reason why someone would do this on a foam model.
maguro is offline Find More Posts by maguro
Reply With Quote
Old Jul 17, 2012, 08:47 AM
Smells like SCIENCE!!!
ibillwilson's Avatar
Canada, ON, Toronto
Joined Jun 2012
341 Posts
Quote:
Originally Posted by maguro View Post
Curling the trailing edge up acts as washout. It causes the tips to stall later than the wing root. Washout is very useful in delaying tip stall on high aspect ratio (long thin) wings and wings with a lot of taper.

The blunt strip on the bottom of the wing will cause turbulent air flow under the wing tip. The results will be high drag and decreased lift at the tip. I can't think of any aerodynamic reason why someone would do this on a foam model.
Ha, so I've got competing effects going on?!

Hmmm... So would there be any use for that strip anywhere on the wing? Perhaps at the root? Would that accentuate the effect of the washout at the tips, or would it be just an increase in drag with no beneficial effect?
ibillwilson is offline Find More Posts by ibillwilson
RCG Plus Member
Old Jul 17, 2012, 11:04 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,695 Posts
"..I had horrible tip stall problems whenever I made a turn at slow speeds..."

You results are very dissimilar to my experiences with wings as you describe. And reports of tip stalling problems on KF wings are almost nonexistent.

I have to wonder if there is not some other issue or issues at play here. Is you plane one of the BB variants or based on one of them? If so, which one? And where was the CG relative to the leading edge and approximate AUW as it was flown?

Also, was the wing incidence at zero relative to the horizontal stabilizer and fusleage center liine?

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Old Jul 17, 2012, 11:57 AM
Smells like SCIENCE!!!
ibillwilson's Avatar
Canada, ON, Toronto
Joined Jun 2012
341 Posts
Quote:
Originally Posted by jackerbes View Post
...
Is you plane one of the BB variants or based on one of them? If so, which one? And where was the CG relative to the leading edge and approximate AUW as it was flown?

Also, was the wing incidence at zero relative to the horizontal stabilizer and fusleage center liine?
...
Hi Jack. The plane that experienced these problems was a 33” BB with 2” monoblock. It originally sported a UC wing, but I eventually replaced that with a KFm3. However, I didn’t bother using the established plan for the 32” BB sport wing, so I ended up building a constant chord wing with tip plates but no washout. CG on that plane was as originally specified for the UC wing, and AUW was about 11 oz. I cut the wing saddle to get 0 degree incidence. I did not change the angle of incidence for the elevator. I still fly RET exclusively.

(Edit: The KFm3 wing did have some dihedral, about one-third of what was specified for the UC wing. Also, it was absolutely huge because it had the same chord as the UC.)

Most of the time, that KFm3 wing flew just fine, but I often had problems with sudden nose dives when doing low-speed turns… like when coming in for a landing. That’s when I started pondering the reason for the taper on the standard UC wing; after a little research, I learned about tip-stall, tip vs root angle of attack, and washout.

Without giving it too much thought, I decided to emulate a wing twist at the tips by adding material to the bottom of the leading edge and curling up the trailing edge. I did not taper the wing at all, so it stayed at constant chord. Problems solved! The plane was able to do fairly tight turns at any speed without abrupt nose dive behaviour. Unfortunately, I made both changes at once, so I didn’t know which alteration had what effect. All I knew is that the two together resulted in a wing with behaviour that I liked.

My current plane is a BB variant of my own “design”… i.e., I butchered Tony65x55’s plan to make something that looked more like a Sherpa bushplane. I built a new 30” KFm3 wing that incorporated those two features from the very start. Still no ailerons, but the plane is actually very nimble… it can turn on a dime at just about any speed and remain well-behaved.

Attached is a picture of my current plane. I snapped this photo before the maiden flight, and before I remembered to add the leading edge bottom strip that I thought I needed.
ibillwilson is offline Find More Posts by ibillwilson
RCG Plus Member
Last edited by ibillwilson; Jul 17, 2012 at 12:00 PM. Reason: additional details
Reply With Quote
Old Jul 17, 2012, 05:55 PM
Build straight - Fly twisty
Whiskers's Avatar
Australia, QLD, Little Mountain
Joined Feb 2010
4,172 Posts
[QUOTE=ibillwilson;22187459]Ha, so I've got competing effects going on?!

Not so. What you have is very similar to a Krueger flap. It, and the reflex will give washout in the tip area.
Washout should really be a root to tip affair, but it is a mixed blessing. In some situations the tips will enter a negative lift mode. Full-size-glider pilots have sometimes been startled to see their wings bending down during high-speed flight.
Most tip stalling is pilot induced. Usually I see it when a plane is flown down-wind at a dangerously low airspeed. It looks to be going quite fast enough but in fact it is teetering on the edge of stalling. As soon as a turn is started the inboard wing stalls.
Whiskers is online now Find More Posts by Whiskers
Reply With Quote
Old Jul 17, 2012, 06:13 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,695 Posts
Sounds like you did all the right things in converting from UC to KFm3. And you fixed the issues so that's that.

Nice looking build on the Sherpa clone, sort of a slimmed down Blu Baby look to it.

I've build several KFm3 and KFm4 wings with no taper in the wings. That was mostly to build flat and while taking advantage of the factory folded edge on sheets of FFF. None of those showed any tip stall tendencies. On the gliders in particular, you really had to pay attention to spot the stalls and recoveries because then were pretty subtle and no dropping wings at all.

Don't be afraid to try another untapered wing, I'd be surprised if you found that same problem again.

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Old Aug 16, 2012, 03:31 PM
Smells like SCIENCE!!!
ibillwilson's Avatar
Canada, ON, Toronto
Joined Jun 2012
341 Posts
In my quest to understand things a little better, I found the following thread talking about the "NASA droop": http://www.rcgroups.com/forums/showthread.php?t=63140

The droop looks a lot like what I did when I added a strip to the bottom of the leading edge. Mine wasn't 40% of the wingspan, however, so I'm not sure how much of an effect it had vs curling up the trailing edge.

Regards!
ibillwilson is offline Find More Posts by ibillwilson
RCG Plus Member
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion ** Kline-Fogleman (KFm) Airfoils - Building/Flying Discussion ** jackerbes Foamies (Scratchbuilt) 7153 Jul 22, 2014 04:20 PM
Cool Here is my KFm-5 DLG GLider (Kline-Fogleman) dougmontgomery Foamies (Scratchbuilt) 151 Apr 21, 2014 09:08 AM
Discussion ** Kline-Fogleman Airfoiled Flying Wing ** Tony65x55 Foamies (Scratchbuilt) 3945 Apr 08, 2014 10:40 AM
Video Kline Fogleman Airfoil on a flying wing Tony65x55 Electric Plane Talk 3 Jan 30, 2009 07:37 PM
Idea Per Dick Kline, Kline-Fogleman test dougmontgomery Hand Launch 49 Apr 13, 2007 02:13 AM